Hitherto, various synthetic rubber latexes and synthetic resin emulsions have been utilized as an improving agent for cement mortars or concretes in the form of a cement-blending polymer dispersion. In general, a nonionic surfactant-containing anionic synthetic rubber latex or a synthetic resin emulsion as dispersed and stabilized in the presence of a nonionic surfactant is employed for the purpose. However, since the surfaces of cement and sand grains are negatively charged (minus-charged) in the presence of water, the rubber latex or resin emulsion is limitative in the functions such as adhesion power under the aqueous condition. Accordingly, development of a cationic polymer dispersion has been desired in this technical field.
As the cationic polymer dispersion, cationic latexes disclosed in Japanese Patent Application Laid-Open No. 52-104549 and Japanese Patent Publication No. 56-26252 have already been put to practical use.
It has been known that the cationic latex is superior to any other anionic or nonionic latex as a cement-blending polymer dispersion, because the former has better water-retentiveness and dispersion stability in blending and also has a higher adhesion strength than the latter.
However, the cationic polymer dispersion which is now commercially sold is one prepared by a method of adding a large amount of an anionic surfactant or a nonionic surfactant to an anionic latex followed by cation-modifying the resulting blend with an alkylamine or aminosilane compound or by a method of adding a large amount of a cationic or amphoteric surfactant to an anionic latex.
The commercial cationic polymer dispersion often have various problems that the quality lowers during storage for a long period of time so that it could no more be cationic and that it could not sufficiently display the functions if the operation order of handling the dispersion is incorrect. In particular, the strength, adhesiveness and durability of the dispersion are noticeably influenced by the ambient condition. Under the above situation, the effect of the conventional or commercial cationic polymer dispersions has heretofore been often considered problematic.